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(114) Longitudinal variability of fish assemblages for evaluating biological integrity of a small urban stream system. Siligato, Simonetta1,2, Böhmer, Jürgen 1, Rahmann, Hinrich1, 1 2 ABSTRACT- Heavy point and non-point pollution as well as stream morphological alteration stresses the aquatic fauna of a small urban stream system. Field investigations conducted in 1998 and 1999 revealed a heavily altered ichthyofaunal assemblage as compared to the potential natural status. Several site specific fish species were missing or present only in very low abundance. Introduced, pollution tolerant and ubiquitous fish species were too abundant. Furthermore, adult fish dominated the populations indicating a disruption of the reproduction cycle. Laboratory investigations on the reproductive organs of stone loach (<1>Barbatula</1> <1>barbatula</1>) revealed no abnormalities while life history strategy may have changed due to altered environmental conditions. To evaluate the biological condition of the stream system we developed an assessment method based on the comparison of the actually established fish assemblage with a reference condition. Results revealed that contaminant influences caused a degradation of biological integrity up to 40 % in the respective stream system. Migration barriers caused loss of habitat as fish were hindered to re-invade depleted river sections. The evaluation of biological integrity by use of fish gives a remarkable impression of the riverine ecosystem health integrating diverse temporal and spatial aspects of the environment. These integrated information on the severity of human caused alterations has to be used to set up proper protection devices as well as restoration efforts. Key words: assessment, biological integrity , fish assemblage, altered stream fauna |
